docs: def _parse_header_code(self):
          """Extract header information and PDB code."""
          code, header = '', ''
          if 'OTHERS' in self.df:
  
              header = (self.df['OTHERS'][self.df['OTHERS']['record_name'] ==
                        'HEADER'])
              if not header.empty:
                  header = header['entry'].values[0]
                  s = header.split()
                  if s:
                      code = s[-1].lower()
          return header, code